| 研究実績の概要 |
BACKGROUND:Hybrid Organic-Inorganic Perovskite (HOIP) materials have achieved rapid success in opto-electronic applications in recent years, with power conversion efficiencies exceeding 23% in solar-cells. However, spatial heterogeneity in film efficiency, due to the presence of defect states remains a major problem. A study of the nanoscale distribution of these defect states, their electronic properties, and the ultrafast photocarrier trapping process at these sites will help improve overall efficiency, and device performance.
PROPOSAL:I proposed to apply our recently developed technique of time resolved photoemission electron microscopy(TR-PEEM)[Nature Nanotech 12, 36(2017),Science Advances 4, eaat9722(2018)] to study the nanoscale spatial distribution of defect states in HOIP films,their electronic structure, and their role in ultrafast photocarrier trapping.
In FY19, we have been able to obtain very clear, high quality images of the defect states using PEEM. We have correlated these PEEM images with high resolution photoluminescence(PL) images and Atomic Force Microscopy(AFM) images. Thereby, we clearly established the role of the defects in device efficiency and that the defects occur exactly at the grain boundaries of the perovskite films. Further, we have been able to generate time-resolved movies of the carrier trapping process at individual defect sites. These movies have revealed the important role of diffusion in the carrier trapping process in perovskite photovoltaic films.The first part of our breakthrough work has just been published in Nature 580, 360(2020).
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| 現在までの達成度 (区分) |
現在までの達成度 (区分)
1: 当初の計画以上に進展している
理由
From the preliminary data, we have been able to make rapid progress in correlating the PEEM images of the defects with other standard techniques such as Photoluminescence and AFM. This ability to simply see the defects, and to correlate their presence with other standard techniques, made it relatively easy to understand some of the important aspects of the defect states.
With these results, our first paper on the work was published in Nature just last month (Nature 580, 360 (2020)).
Thus, we believe that we progressed more smoothly than originally expected.
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| 今後の研究の推進方策 |
Electronic structure of defects: The rapid initial success is being followed up by a more detailed understanding of the electronic structure of defects. By providing detailed, spatially resolved maps of the work-function, we are trying to understand the chemical nature of the defect states.
Time Dynamics of Trapping: Our first results in studying the time dynamics revealed the important role of diffusion in the trapping process. We now attempting to obtain higher quality data to look at the trapping process at individual nanoscale traps and to understand the relationship to trap density and location relative to grain boundary and intra-grain diffusion.
Other photovoltaic materials: The first studies were applied to state-of-the-art photovoltaic materials - triple cation mixed halide perovskite films. We are all planning to extend our studies to other perovskite photovoltaic materials, e.g. lead-free photovoltaics.
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| 次年度使用額が生じた理由 |
Due to the rapid and unexpected success of the measurements, significant work in FY19 was conducted in analyzing data and preparing for publication. As a result, expenditures for consumables and equipment was lower than expected, and carried over into the following year. This year, we expect increased expenditure for consumables (chemicals and associated preparation materials) related to sample preparation and sample testing to make the next set of samples. We also expect to require consumables (optics, opto-mechanics and vacuum parts) to improve optical and electron microscopy setup in order to improve signal-to-noise in the measurements. A part of the grant money carried over from FY19 will also be used to pay the publication fee and associated expenses, which fall into FY20 due to final publication date of April 2020.
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